[Tagging] boundary=town, place=town

[Pierre-Alain Dorange]

Steve Bennett <stevagewp at gmail.com> wrote:

> > a node (place=town or village, depending on population size)
> >
> > a relation (type=boundary + boundary=administrative + admin_level=8)
> > The relation has members :
> > outer/inner composed with ways that define the boundary (a closed way
> > defining an area)
> > and a node (role=admin_centre) defining the node (place) that is the
> > center of the town (usely the main place in the town, an indicator for
> > rendering the name for example.
> 
> Hmm, interesting. Why don't you use the place=town node to mark the
> centre of town? (Presumably you mean "place" in the French sense of
> "town square").

The node place=town is the center of town (also used as role
"admin_centre" for the boundary relation).
There is only one physical node.

And yes i used "place" in the french sense : main city center, town
square. Sorry ;-)

http://en.wikipedia.org/wiki/Town_square

> Also, this makes me think that boundary=town was a shorthand for
> boundary=administrative,admin_level=8. Sort of makes sense.

boundary=town is not documented (and not used) and must not been used
(IMHO), because admin_level=8 is widespread.

According to taginfo.openstreetmap.de :

admin_level=8
        96 502 relations
        290 837 ways
        13 665 nodes (!?)
boundary=village        30
boundary=city_limit     53
boundary=hamlet 37
boundary=town   0
         
> Although...that just raises a different question: what's the
> difference between a town mapped out as an area (place=town) and a
> town mapped with a boundary=administrative, admin_level=8 (plus
> relation).

I don't understand, i don't know about area (place=town), place=town is
only node for me. I don't know the usage area (a way ?) it seems odd for
me. 
i prefer far more multiples ways linked into a relation than a single
way, because with relation we just have a build one way for frontier
between 2 area (2 town for example) and the way can be linked into the 2
relations (one relation per town) to define the boundary. Using only one
way for boundary leeds to draw mutlple time boundary with same nodes ?
Or using the old way using right and left ?

If you ask about different betwen the node and the relation :
No difference, that's 2 views for the same thing.
The node is the center of the town, the relation is the boundary.
One geographical object (town), 2 representations for different usages.

The data (name, population, ref and so on) can be attached (once) to the
node or the relation. Actual usage is to put the name in the obth object
because nto all application used relation.

> I guess there is no difference, just two different ways of expressing
> the same thing. 

yes, for different usage. 
The node can be used to display the name (render) or for directions
(going from A to B). The relation (boundary) can be used by nominatic to
build adresses (or any other application), to draw the boundary
(render), to check is an onject is in a boundary, to display the town
area, etc...
In this model (boundary relation) the node can be used alone, or as the
role admin_centre of the relation.
I think it's a powerful model and it works fine, IMHO.

-- 
Pierre-Alain Dorange
OSM experiences : <http://www.leretourdelautruche.com/map/>